To understand and use depth of field you should realize that depth of field is the area behind and in front of your focusing point - the thing or object you are shooting. Depth of field is determined by apreture or f -stop, the shutter speed of your camera and the focal length of the lens. If you have the right combination of shutter speed and the f-stop, your picture will have the right exposure. If you change either the f-stop or the shutter, you need to remember to adjust the other! Different lens will effect different shutter speed. The longer the lens is the slower the shutter speed will be. If your shutter speed is too slow, you may need to put your camera on a tripod because of this, due to your shaking.